JP2015516882A - Method and system for purifying exhaust gas from an internal combustion engine - Google Patents

Abstract

The present invention provides a method and system for purifying exhaust gas from an internal combustion engine and a system comprising a filter and an SCR catalyst. The filter is periodically regenerated, increasing the temperature of the exhaust gas to 850 ° C. and increasing the water vapor content to 100% by volume. The SCR catalyst is a hydrothermally stable zeolite and / or zeotype having an AEI type framework and promoted with copper.

Description

  The present invention relates to after treatment of exhaust gas from an internal combustion engine in terms of removal or reduction of harmful compounds. More particularly, the present invention focuses on the removal of particulate matter and the reduction of nitrogen oxides in exhaust gas from lean burn internal combustion engines, particularly diesel engines.

  Lean burn engines are known for their energy efficiency, but have the disadvantage of forming particulate matter and nitrogen oxides that must be removed or at least reduced in the exhaust gas.

  In order to prevent environmental pollution and meet some governmental requirements, modern diesel engines include oxidation catalysts for removing volatile organic compounds, particulate collection filters for removing particulate matter, and An exhaust gas purification system that sequentially includes a catalyst that is active for selective reduction of nitrogen oxides (NOx) is provided.

  It is also known to incorporate an SCR catalyst into a particulate collection filter.

  Selective catalytic reduction of NOx in the exhaust gas is usually accomplished by reaction with ammonia introduced by itself or as a precursor thereof, which can be nitrogen oxides, mostly nitrogen dioxide and monoxide. Nitrogen (NOx) is introduced into the exhaust gas upstream of the SCR catalyst for selective catalytic reduction of nitrogen to nitrogen.

  A number of catalyst compositions have been disclosed in the literature for this purpose.

  In recent years, zeolites promoted with copper or iron have shown great interest, especially for use in automotive applications.

Zeolite catalyst containing copper for NH ₃ -SCR applications have shown a high activity at low temperatures. However, in some applications, the catalyst may be exposed to high temperature fluctuations in the exhaust gas. In addition, the exhaust gas contains a high concentration of water vapor from the combustion engine, which may degrade the performance of the zeolite catalyst. One mechanism by which the catalyst can be deactivated is its decomposition due to the instability of the framework structure of the zeolite to hydrothermal conditions, which is further enhanced by the presence of copper, so hydrothermal stability is This is a problem related to a copper-based zeolite catalyst.

Deactivation of copper-containing zeolite catalysts in NH ₃ -SCR applications is typically due to the decomposition of the structure due to the instability of the framework structure of the zeolite to hydrothermal conditions. The thickness is further enhanced by the presence of copper. However, its stability is particularly important for automotive applications where the catalyst undergoes high temperature fluctuations in an exhaust gas stream containing water.

  Deactivation of the catalyst is a particular problem in exhaust gas purification systems provided with a particulate collection filter that must be periodically regenerated actively to prevent pressure build-up across the sooted filter.

  Active regeneration is performed by the burning of trapped soot. The regeneration can be initiated by introducing fuel into the exhaust gas upstream of the oxidation catalyst or by electrically heating the particulate collection filter.

  During active regeneration, the temperature of the exhaust gas at the outlet of the filter reaches over 850 ° C. and the water vapor content for a period of 10-15 minutes, depending on the amount of soot trapped in the filter Can reach over 15% and up to 100%.

US Pat. No. 5,958,370

J. et al. Chen, J.A. M.M. Thomas, P.M. A. Wright, R.W. P. Townsend, Catal. Lett. 28 (1994) [241-248]

  Nitrogen oxides in contact with hydrothermal stable catalyst when exposed to high temperature and high water vapor concentration during active regeneration of the particulate collection filter and particulate collection filter using the particulate collection filter It is a general object of the present invention to provide a method for removing harmful compounds from lean burn internal combustion engines, such as nitrogen oxides, by selective catalytic reduction.

  The object of the present invention is a hydrothermally stable zeolite or zeotype having an AEI type skeleton, and the skeletal structure has a structure under aging conditions with hot water even when copper is present in the zeolite or zeotype. We have found that this can be achieved by using the zeolite or zeotype retained.

In accordance with the above findings, the present invention
Reducing the soot content in the exhaust gas by passing the exhaust gas through a particulate collection filter;
Subsequently reducing the content of nitrogen oxides in the presence of ammonia or its precursor by contact with a catalyst active in NH3-SCR;
Periodically regenerating the filter by burning the soot trapped in the filter and thereby increasing the temperature of the exhaust gas to 850 ° C. and increasing the water vapor content to 100% by volume; and Passing the exhaust gas from the filter through a catalyst during regeneration, wherein the catalyst has an AEI type skeleton and copper is incorporated into the skeleton, which is hydrothermally stable. The process comprising a zeolite and / or a zeotype,
A method for purifying exhaust gas from an internal combustion engine is provided.

  “Hydrothermally stable” means that after the zeolite and zeotype catalyst has been exposed to a temperature of at least 600 ° C. and a water vapor content of up to 100% by volume for 13 hours, the catalyst has an initial surface area of at least 80- 90% and 80-90% of the micropore volume, and at least 30-40% of the initial surface area and micropore volume after exposure to a temperature of at least 750 ° C. and a water vapor content of up to 100% by volume for 13 hours It has the ability to maintain

  Preferably, the hydrothermally stable zeolite or zeotype having an AEI type skeleton has an atomic ratio of silicon to aluminum of 5 to 50 for zeolite or 0.02 to 0.5 for zeotype.

  The most preferred zeolite or zeotype catalysts for use in the present invention are the zeolite SSZ-39 and the zeotype SAPO-18, both of which are "AEI" into which copper has been introduced by immersion, liquid ion exchange or solid ion exchange. Has a skeletal structure.

  The atomic ratio of copper to aluminum is preferably about 0.01 to about 1 in the case of zeolite. For the zeotype, the preferred atomic ratio of copper to silicon is correspondingly 0.01 to about 1.

  By utilizing the above-described catalyst employed in the present invention, after aging at 750 ° C., 80% of the initial reduction rate of NOx at 250 ° C. is maintained compared to 20% of the Cu—CHA catalyst.

  Thus, in an embodiment of the present invention, after the catalyst has been exposed to a temperature of 750 ° C. and 100% water vapor content in the exhaust gas for 13 hours, 80% of the initial reduction rate of nitrogen oxides at 250 ° C. is maintained. Is done.

  The present invention further provides an actively regenerating particulate collection filter, and an SCR catalyst having an AEI type framework and promoted with copper, hydrothermally microporous stable zeolite and / or zeotype. An exhaust gas purification system is provided.

  In one embodiment of the exhaust gas purification system according to the present invention, the SCR catalyst is incorporated into a particulate collection filter.

  In a further embodiment, the atomic ratio of copper to aluminum is about 0.01 to about 1 for zeolites, and for the zeotype, the atomic ratio of copper to silicon is 0.01 to about 1.

  In another embodiment, the atomic ratio of silicon to aluminum in the SCR catalyst is 5-50 for zeolite and 0.02-0.5 for zeotype.

  In a further embodiment, the SCR catalyst provides 80% of the initial reduction rate of nitrogen oxides at 250 ° C. after the catalyst has been exposed to a temperature of 750 ° C. and 100% water vapor content in the exhaust gas for 13 hours. maintain.

  In a further embodiment, the SCR catalyst maintains 80-90% of the initial microporosity after aging at 600 ° C and 30-40% of the initial microporosity after aging at 750 ° C.

  In another embodiment, the SCR catalyst is aluminosilicate zeolite SSZ-39 and / or silicoaluminophosphate SAPO-18.

  In the above embodiment, the SCR catalyst can be deposited on a monolithic support structure.

  The Cu-SSZ-39 catalyst system showed improved performance compared to a typical "conventional" Cu-SSZ-13 when compared to a similar Si / Al ratio.

It is a figure which shows the pattern of the powder X-ray diffraction of Cu-SSZ-39 after calcination by this invention. It is a figure which shows the pattern of the powder X-ray diffraction of Cu-SSZ-39 after calcination by this invention. It is a figure which shows the conversion rate of NOx which exists in the gas which leaves a reactor. FIG. 3 is a diagram showing the conversion of NOx present in the gas exiting the reactor according to the present invention.

Example 1: Preparation of Cu-SSZ-39 catalyst As described in US Pat. No. 5,958,370 using 1,1,3,5-tetramethylpiperidinium as an organic template. Zeolite SSZ-39 having a framework code AEI was synthesized in the same manner as described above. A gel having the following composition: 30Si: 1.0Al: 0.51NaOH: 5.1OSDA: 600H ₂ O is autoclaved at 135 ° C. for 7 days, the product is filtered, washed with water and air Dried and calcined in. The final SSZ-39 had Si / Al = 9.1 as measured by ICP-AES.

To obtain Cu-SSZ-39, the calcined zeolite was ion exchanged with Cu (CH ₃ COO) ₂ to obtain the final catalyst with Cu / Al = 0.52 after calcination.

  The powder X-ray diffraction (PXRD) pattern of Cu-SSZ-39 after calcination is shown in FIG.

Example 2: NO of test 500ppm of the catalyst, consisting of 5% _{H 2} O of _NH 3, 7% of _O 2, _{N 2} in 533Ppm, to simulate the engine exhaust gas stream with a total flow rate of 300 mL / min First, the sample activity was tested in a solid bed reactor for selective catalytic reduction of NOx, and 40 mg of catalyst was tested.

  The NOx present in the gas exiting the reactor is continuously analyzed and the conversion is shown in FIG.

Example 3 Test for Hot Water Durability To test the hot water stability of the zeolite, the sample was steamed. Samples were exposed to a supply of water (2.2 mL / min) in a conventional furnace at 600 ° C. or 750 ° C. for 13 hours and then tested as in Example 2.

  The catalyst results are also seen in FIG. Samples that had undergone hydrothermal treatment were marked at 600 or 700 ° C., depending on the temperature used during the hydrothermal treatment.

  Further characterization was also performed on all processed samples. The PXRD pattern after hydrothermal treatment is shown in FIG. 1, and the BET surface area, micropore area, and micropore volume of the treated sample are summarized in Table 1 below.

Example 4: Comparative Example molecular composition of the Cu-CHA (Cu-SSZ- 13), SiO 2: 0.033Al 2 O 3: 0.50OSDA: 0.50HF: 3H 2 O ( wherein, OSDA is N, Cu-CHA zeolite was prepared from a gel with N, N-trimethyl-1-adamant ammonium hydroxide.

  The gel was autoclaved under rotation at 150 ° C. for 3 days to obtain a final zeolite product with Si / Al = 12.7 after washing, drying and calcination.

To obtain Cu-CHA, the calcined zeolite was ion exchanged with Cu (CH ₃ COO) ₂ to obtain the final catalyst with Cu / Al = 0.54 after calcination.

  The powder X-ray diffraction (PXRD) pattern of Cu-CHA after calcination is shown in FIG.

  This catalyst was also tested according to Example 2 and evaluated for hot water durability as in Example 3. The catalyst results are summarized in FIG. 2 of the drawings. The PXRD pattern of the treated CHA sample is shown in FIG. 1 and the tissue properties (BET surface area, micropore volume and micropore area) are summarized in Table 1.

Example 5: Cu-SAPO-18
Silicoaluminophosphate SAPO-18 having the skeletal code AEI is described in [J. Chen, J.A. M.M. Thomas, P.M. A. Wright, R.W. P. Townsend, Catal. Lett. 28 (1994) [241-248] (Non-Patent Document 1), and 2% by weight of Cu was immersed. The final Cu-SAPO-18 catalyst was treated hydrothermally at 750 ° C. in 10% H ₂ O and 10% O ₂ and tested under the same conditions as given in Example 2. . The results are shown in FIG.

Claims (14)

A method for purifying exhaust gas from an internal combustion engine, the method comprising:
Reducing the soot content in the exhaust gas by passing the gas through a filter;
Subsequently, reducing the content of nitrogen oxides in the presence of ammonia or a precursor thereof in contact with a catalyst active in NH3-SCR,
Periodically regenerating the filter by burning the soot trapped in the filter and thereby increasing the temperature of the exhaust gas to 850 ° C. and increasing the water vapor content to 100% by volume; and Passing the exhaust gas from the filter through a catalyst during regeneration, wherein the catalyst has an AEI type framework and is promoted with copper, hydrothermally microporous stable zeolite and And / or the process comprising a zeotype,
Including the above method.   The copper to aluminum atomic ratio for the zeolite is from about 0.01 to about 1, and the copper to silicon atomic ratio for the zeotype is from 0.01 to about 1. The method described in 1.   3. A process according to claim 1 or 2, wherein for the zeolite, the atomic ratio of silicon to aluminum is 5-50 and for the zeotype it is 0.02-0.5.   The catalyst is maintained at 80% of the initial reduction rate of nitrogen oxide at 250 ° C after being exposed to a temperature of 750 ° C and 100% water vapor content in the exhaust gas for 13 hours. 4. The method according to any one of 3.   The method according to any one of claims 1 to 4, wherein at least 80-90% of the initial microporosity is maintained after aging at 600 ° C and at least 30-40% is maintained after aging at 750 ° C. .   The process according to any one of claims 1 to 5, wherein the catalyst is aluminosilicate zeolite SSZ-39 and / or silicoaluminophosphate SAPO-18.   An exhaust gas purification system comprising an active regenerative particulate collection filter and an SCR catalyst having an AEI type framework and comprising a hydrothermally microporous stable zeolite and / or zeotype promoted with copper.   An exhaust gas purification system in which the SCR catalyst is incorporated in the particulate collection filter.   9. The atomic ratio of copper to aluminum is about 0.01 to about 1 for the zeolite and the atomic ratio of copper to silicon is 0.01 to about 1 for the zeotype. The exhaust gas purification system described in 1.   The exhaust gas purification according to any one of claims 7 to 9, wherein for the zeolite, the atomic ratio of silicon to aluminum is 5 to 50, and for the zeotype it is 0.02 to 0.5. system.   The SCR catalyst is maintained at a temperature of 750 ° C and 100% water vapor content in the exhaust gas for 13 hours, maintaining 80% of the initial reduction rate of nitrogen oxides at 250 ° C. 10. The exhaust gas purification system according to any one of 10 to 10.   The SCR catalyst maintains at least 80-90% of the initial microporosity after aging at 600 ° C and maintains at least 30-40% of the initial microporosity after aging at 750 ° C. The exhaust gas purification system as described in any one of -11.   The exhaust gas purification system according to any one of claims 7 to 12, wherein the catalyst is an aluminosilicate zeolite SSZ-39 and / or a silicoaluminophosphate SAPO-18.   The exhaust gas purification system according to any one of claims 7 to 13, wherein the SCR catalyst is deposited on a monolithic support structure.

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